A spark plug for an internal combustion engine such as a vehicle engine includes, for example, a center electrode, an insulator provided on the outside thereof, a cylindrical metal shell provided on the outside of the insulator, and a ground electrode of which a base end portion is joined to the front end surface of the metal shell. The inner surface of the front end portion of the ground electrode is disposed to oppose the front end portion of the center electrode, and accordingly, a spark discharge gap is formed between the front end portion of the center electrode and the front end portion of the ground electrode.
Recently, it is considered that tips (precious metal tips) made of precious metal alloys can be joined to the front end portions of the center electrode and the ground electrode to achieve an improvement in spark consumption resistance in addition to an improvement in ignition performance and spark transmission. Further, there is a technique in which in order to achieve an increase in the joining strength between a precious metal tip and a ground electrode, the precious metal tip for the ground electrode is joined to an intermediate member, and the intermediate member is joined to the ground electrode (for example, refer to Patent Documents 1 and 2). In the technique, the intermediate member and the precious metal tip are joined with a fused part formed of the metal of the two fused together.    [Patent Document 1] JP-A-2004-134209    [Patent Document 2] JP-A-8-298178